Control system for tire building

ABSTRACT

A control system for tire building wherein a first ply of fabric is wrapped around a rotating drum and thereafter additional &#39;&#39;&#39;&#39;work&#39;&#39;&#39;&#39; is done in relation to the first and subsequently wrapped plies and other tire components. The rotational speed of the drum controls the movement of other mechanical devices which perform the additional &#39;&#39;&#39;&#39;work.

United States Patent Homa et al. 1451 Aug. 15, 1972 [54] CONTROL SYSTEMFOR TIRE [56] References Cited BUILDING UNITED STATES PATENTS 1Inventors George H9ma, Northfield; 3,244,575 4/1966 Sabo m1. ..lS6/l32 1North Canton; 3,568,072 3/1971 Rosener ..318/571 M111", Tallmadge, of3,530,283 9/1970 McDaniel ..318/57l 3,414,787 12/1968 Reuteleretal...318/570 3,356,994 12/1967 Elbling ..3l8/569 [73] Assignee: AkronStandard, division of h Indusmes Inc-7 Cmcmnatl, Primary ExaminerThomasA. Robinson Ohm AttorneyMack D. Cook [22] Filed: Aug. 19, 1970 [57]ABSTRACT A control system for tire building wherein a first ply of [21]Appl 65208 fabric is wrapped around a rotating drum and thereafteradditional work is done in relation to the first and subsequentlywrapped plies and other tire [521 u.s.c1. ..235/154,3l8/569, 23541 5 121 components The rotational Speed of the drum com 51 Int. Cl. ..G06f15/45 mmemem Of (her mechanical devices which perform the additionalwork. [58] Field of Search .156/132, 401; 235/l5l.l l, 154;

318/567, 569, 570, 571, 579 6 Claim, 4 Drawing Figures FLIP FLOP TIMERINPUT 0/001: NAND DRUM fTBM PROGRAM MATRIX GATE DRUM a MEANS DECODERLOGIC MODULE I2 MOTOR CONTROL STITCHER snrcwsn MODULE sous/vow FLO/ZDRIVER so1 1:-o1os LOG! CONTROL SYSTEM FOR TIRE BUILDING BACKGROUND OFTHE INVENTION The present invention relates to the efficient and precisebuilding of an unvulcanized tire on a rotating drum. Building of a tireon a rotating drum requires sequential performances of numerous workfunctions beginning with and subsequent to wrapping a first ply of tirefabric around the drum. Techniques for building a tire using a rotatingdrum are well known in the prior art. See a 1951 patent to L. C.Frazier, U. S. Pat. No. 2,567,064, which describes techniques forbuilding a tire on a rotating drum of the radial expanding type withpneumatic bladder turn up for wrapping the bead wire components of thetire.

The building of a tire involves both dimensional and dynamic factors.The various components of a tire, inner liner, body plies, beads, chaferstrips, breaker plies, tread stock, etc., must each be placed around thebuilding drum in a precise and exact laminate relation. At each stage ofcomponent placement, pressure forces are applied to adhere thecomponents to each other so that a dimensionally precise structure maybe removed from the building drum and transported to the vulcanizationpress.

Heretofore, various work" functions in building a tire on a rotatingdrum have been mechanized or semi-automated. Control systems do existwherein the operator may initiate one or more of the devices associatedwith the building drum merely by pushing a button. These prior systems,while tending to increase productivity have nevertheless not beenresponsive to the dimensional and dynamic factors involved in tirebuilding.

SUMMARY OF THE INVENTION The object of the invention is to provide acontrol system for the efficient and precise building of an unvulcanizedtire on a rotating drum. More particularly, the object is to provide acontrol system for the performance of numerous work" functions beginningwith and subsequent to wrapping a first ply of tire fabric" around thedrum. Specifically, it is an object to provide a control system whereinthe rotational speed of the drum controls the movement of devices whichperform the work" functions so as to observe, recognize and correlatethe dimensional and dynamic factors involved in the proper building of atire on a rotating drum.

These and other objects of the invention, as well as the advantagesthereof, will be apparent in view of the description of a preferredembodiment for control of the stitching" operation in the tire buildingsequence, as set forth in detail below.

In general, a control system according to the invention is used with atire building machine wherein a first ply of fabric is wrapped around arotating drum and thereafter work devices associated with the drumsequentially perform operations upon the first ply and other tirecomponents, comprising, input program means providing coded commandsrelating to a specific operation in the tire building sequence, matrixdecoder means receiving and recognizing said coded commands andproviding outputs to activate circuitry to accomplish an operation inthe tire building sequence, timer means controlling an output of saidmatrix decoder means so that said output is provided only at selecttimes, drum control means capable of receiving an output of said matrixdecoder means and operating the tire building drum accordingly, and workdevice control means capable of receiving an output of said matrixdecoder means and operating the work device accordingly.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the controlsystem according to the concepts of the present invention.

FIG. 2 is a block diagram of the timer module shown in FIG. 1.

FIG. 3 is a block diagram of the drum module and control circuitry shownin FIG. 1.

FIG. 4 is a block diagram of the stitchcr module and control circuitryshown in FIG. I.

DESCRIPTION OF A PREFERRED EMBODIMENT A control system according to theinvention, referred to generally by the numeral 10, is used with a tirebuilding machine (TBM) having drum 11 with a generally cylindricalworking surface 12. Reference is made to US. Pat. No. 2,567,064 for suchfurther details as may be necessary to understand the techniques ofbuilding a tire on a rotating drum 11.

System 10 is provided with an input program means 15 which can take anyof a number of conventional forms. For example, paper or metallic tapecan be utilized wherein decimal numbers are punched in binary coded formusually in an eight channel configuration. A conventional photoelectrictape reading device can convert the coded program into electronicsignals which may then be fed to a diode matrix decoder 16, a highsignal, on the order of l6 volts, being provided if a hole is present ina channel and a low signal, on the order of one-half volt, beingprovided if no hole is encountered in the particular channel.

The decoder 16 consists of a number of positive AND gates which as iswell known in the art, will generate a pulse only during thesimultaneous occurrence of two or more other pulses. Through these ANDgates, the matrix decoder 16 converts the signals from the input programmeans 15 into a single conventional decimal number. This numbercorresponds to a specific machine function, in this case a step in thetire building sequence. For example, if the decoder 16 reads the numeral21 from the input program means 15, this can be made to correspond to abead setting step. When the signal from the input program means 15 isdecoded and one conventional decimal number obtained, a wirecorresponding to that number is supplied with a high voltage. Throughthese independent wires, the matrix 16 activates circuitry to achievethe desired function in a manner to be hereafter described.

Certain of the coded function signals from the matrix decoder 16 are fedto one of a plurality of flip-flop circuits 17 which in turn, activatethe timer module 20. As will be hereinafter explained, the flip-flopcircuits 17 when once activated or set by the matrix decoder 16 arereset at the end of a timing period by the timer module 20. The signalsfed directly to the timer module through the flip-flops 17 from decoder16 are those signals which correspond to steps in the tire buildingsequence which must be timed independently, that is,

those steps do not themselves provide a completion signal of their own.As will hereinafter be described, the completion signal is an end ofoperation signal having many sources for the purpose of advancing theinput program means 15 to the next command.

The timer module 20, best seen in more detail in FIG. 2, consists of aseries of electrical components which establishes machine functiontiming periods and also provides enable/disable signals to the diodematrix 16. The latter function allows the matrix 16 to read the code ofthe input program means 15 only when the input or tape is motionless.Thus the timer module 20 disables the matrix 16 during periods of tapetransfer.

Timer module 20 receives one of a plurality of inputs from the output ofthe flip-flop circuits 17, one of the inputs being high and the otherbeing low," since the diode matrix 16 is capable of putting out on anindividual line only one high signal at a time. To prevent interactionbetween the outputs of circuits 17, each timer module 20 input isisolated from the other by diodes 21 in a standard manner. The thusisolated high" input is provided to one of a plurality of variableresistor potentiometers 22 which then activates a constant currentgenerator 23. The activation of constant current generator 23 beginscharging the timing capacitor 24, the charge of which increases linearlywith time at a rate determined by the setting of the particular variableresistor potentiometer 22.

When the timing capacitor 24 reaches a certain voltage level, forexample, volts, a unijunction transistor 25 is caused to fire producingan output pulse. The leading edge of this pulse is used, through astandard OR gate 26, to trigger two one-shot multivibrators 27 and 28.Multivibrator 27 provides a pulse of short duration on the order of 1.5millisecond and is fed back to the input program means to control theadvance of the program. When the program is magnetic tape, for example,the short one-shot multivibrator 27 causes the tape drive mechanism toadvance one tape line. Multivibrator 28 provides a much longer pulse, onthe order of milliseconds, which is considered the disable signal inthat it prevents functioning of the diode matrix decoder 16 when thetape or other program is moving.

As is well known in the art, the OR gate 26 is a diode device which willconduct when a voltage is present at one of a plurality of inputs. Thus,as just described, when a pulse appears from unijunction transistor 25,an output will appear from OR gate 26. Likewise, the OR gate 26 will besatisfied if a pulse appears from an external input shown in FIG. 2.This external input is in the form of an operation completion signalfrom other portions system 10, the details of which being hereinafterdescribed.

When not disabled by the timer module 20 as just described, other highand low signals from the diode matrix decoder 16 can be fed to a NANDgate logic system 18. These signals, differentiated from those that goto flip-flops 17, are those corresponding to steps in the tire buildingsequence for which no timing interval is needed, a completion signalbeing provided at the end of the specific step. Of course, only one highsignal on a specific wire can be provided at one time. This high signalis combined with other inputs (not shown) to an AND gate which providesa high" output if the signal from decoder 16 and all other inputs ishigh; otherwise, the circuit would be disabled" in a low output state.These other inputs" are in this instance inputs provided as highs" onlywhen certain physical conditions are met.

For example, in a bead setting step, a certain wire would have a highsignal thereon and be provided to the NAND gate 18. However, no outputwould appear from the NAND gate unless other inputs thereto would behigh." These other inputs would, in this instance, correspond to certainphysical conditions, to wit: the drum must be locked from rotation; thestitcher must be in a retracted position; the drum must be expanded;etc.

Drum module 30, called such because of its environmental associationwith a tire building drum, is shown in more detail in FIG. 3, beingenclosed in the dotted lines. The primary functions of drum module 30are providing for rotation of the tire building drum from any startingpoint through a preset number of degrees, positioning the drum to aspecific controllable point from a known starting point, and merelyproviding for drum revolution at a preset speed during stitching andwork operations.

The positioning function is utilized to provide a plurality of startingpoints around the drum for ply application. This prevents the bulkybuild-up of ply splices which would occur if each ply of fabric began atthe same point on the drum. A plurality of controllable positions can beprovided for, each being established by the setting of a potentiometer31. Each potentiometer setting is referenced to what can be called adrum zero position. This position is a starting point which is sensed bya photocell circuitry 32. Dependept on the setting of a particularpotentiometer 31, the drum will rotate the desired number of degreesfrom the drum zero position upon command.

When the input program means 15 orders a ply application function, theappropriate signal is transferred to the drum module 30 as previouslydescribed. A relay 33 then closes the circuit causing the voltage on thespecific potentiometer 31 to be imposed on an integrating amplifiercircuitry 34, which, of course, includes a charging capacitor. Amplifiercircuitry 34 can be designed so that the voltage across the chargingcapacitor builds up almost instantaneously. This voltage actuates themotor control 40 to drive the drum 1]. Motor control 40 is a solid statebidirectional and regenerative system which operates the drum andstitcher motors on command.

A tachometer generator 35 is coupled to the drum 1 l and feeds back tocircuitry 34 a voltage corresponding to drum speed' This voltage is,however, fed back only after the drum zero photocell signal means 32 hasWhen a rotation function is commanded by the input program means notreferenced to drum zero, similar circuitry is activated. In thisinstance, the particular potentiometer 31 is again set to provide forthe desired angular revolution and relay 36 is immediately energizedinstead of waiting for the drum to pass the drum zero position. Thus,the rotation function is accom plished from any starting point.

Whether providing one drum revolution or positioning the drum to acontrollable point, upon the completion of the function a signal isprovided through standard comparator circuitry (not shown) to activatethe timer module in a manner previously described.

The function of drum running at a constant speed is controlled directlyfrom the NAND gates 18 through flip-flop memory logic 37. When aflipflop 37 is set, a drumrun potentiometer voltage 38 is imposed on themotor control circuitry to run the drum accordingly.

Certain of the lines from the NAND gate 18 are provided to the stitchermodule 60, the stitcher 14 being one of the work devices referred toabove. These lines, of course, carry signals which correspond to thosesteps in the tire building sequence which relate to stitching functions.Such functions can be broken down into two categories: positioning orprepositioning of the stitcher 14 and actual stitching.

When it becomes desirable to position the stitcher 14 at a particularlocation, for example, in preparation for a white sidewall stitchingoperation, the appropriate signal from the input program means 15 wouldbe transferred through the NAND gate logic 18 to the stitcher module 60enclosed in dotted lines in FIG. 4. Such a signal closes one of aplurality of position relays 61 which latches in and imposes a signalfrom a position potentiometer 62 onto a conventional differential I orerror amplifier 63. This voltage into amplifier 63 represents the analogof desired stitcher position. This, of course, can be preset accordingto certain parameters, such as the size or design of the tire beingbult.

The voltage out of amplifier 63 is increased and inverted by anotheramplifier 64 which then, through the motor control 40, previouslydescribed, operates the stitcher 14. A feedback potentiometer 65monitors the position of the stitcher 14 and presents a feedback voltageto error amplifier 63. As in any standard closed loop position servosystem, the input to amplifier 63 (the desired stitcher location) iscompared with the feedback signal (actual stitcher location) and anyerror existing operates the stitcher movement until such time that noerror exists, the stitcher being in the proper position. When suchposition is reached, an absolute value comparator 66 disconnects thelatch-in of relay 61 and provides an operation complete signal to thetimer module 20.

When an actual stitching function is called for by the input programmeans 15, the closing of the appropriate relay 67 imposes the voltagepreset on stitch potentiometers 68. A relay 69 is also energized causingthe signal from the drum tachometer generator 35 to be sensed byamplifier 64. At this same time amplifier 64 becomes disconnected fromerror amplifier 63 by the opening of a contact therebetween (not shown).Thus, amplifier 64, which acts as an operational amplifier, is connectedonly to the drum tachometer generator cir' curt.

The linear speed of the stitcher 14 is thus directly controlled by thespeed of the drum. Therefore, if the drum speeds up, as by an adjustmentof the drum-run potentiometer 38, the stitcher 14 also moves fastermaintaining the same lap ratio. The end result is that all portions ofthe area being stitched are stitched uniformly. The actual lap ratio canbe adjusted and controlled by potentiometer circuitry 70 so that thestitcher speed can be varied for any particular drum speed. For example,settings can be accomplished wherein the stitcher 14 moves a lineardistance along the axis of the drum an equivalent of one-fourth itswidth for every drum revolution.

It may also often be desirable to regulate or change the radially inwardpressure of the stitcher 14 as it performs various stitching operations.Normally the stitcher is operating at what can be called a highpressure. lf, however, at a certain point in the stitching operation itis desirable to change to a low pressure, a position potentiometer maybe set to perform that function. The voltage on potentiometer 80 is madeto correspond to the position at which the pressure is to change. Thisvoltage is provided to a pressure error amplifier 81 which like erroramplifier 63 compares the desired input with the actual position signalas provided by feedback potentiometer 65. When the desired position isreached, a pressure switch 82 is actuated changing the pressureaccordingly. This switch is reset at the end of the particular stitchingfunction.

Those steps in the tire building sequence which have no direct relationto drum rotation or stitcher position, for example, bead setting orbladder inflating, are, when commanded by the input program means 15,sent by decoder 16 to flip-flop logic circuitry 19. Like flipflop 17,circuitry 19 serves as a memory gate to activate the solenoid drivercircuit 90.

The input stage of the solenoid driver is a basic inverter while theoutput stage is a power transistor switch which energizes the propersolenoid coil 91 by completing the circuit. Operation complete signalscan again be provided to the timer module 20 to signal the tape advancemechanisms for continued automatic operation.

It should now be evident that when the subject control concept isutilized with a tire building machine, more efficient and precise tiremanufacturing can be accomplished.

We claim:

1. A control system (10) for a tire building machine including acylindrical drum (11) and work devices wherein a first ply of fabric iswrapped around the rotating drum and thereafter the work devicesassociated with the drum sequentially perform operations upon the firstply and other tire components comprising, input program means (15)providing coded commands relating to a specific step in the tirebuilding sequence, matrix decoder means (16) receiving and recognizingsaid coded commands and providing outputs to activate circuitry toaccomplish an operation in the tire building sequence, timer means (20)controlling an output of said matrix decoder means so that said outputis provided only at select times, drum control means (30) capable ofreceiving an output of said matrix decoder means and operating the tirebuilding drum accordingly,

said drum control means including integrating amplifier means (34)having a charging capacitor, position potentiometer means (31) chargingsaid capacitor with a charge representing the desired amount of rotationof the drum, tachometer generator means (35) providing a signal which isthe analog of drum rotation, said signal from said tachometer generatormeans discharging said capacitor, and motor control means (40) rotatingthe drum as long as a charge appears in said capacitor, whereby saiddrum is rotated according to the setting of said position potentiometermeans,

and work device control means capable of receiving an output of saidmatrix decoder means and operating a work device accordingly.

2. A control system according to claim 1 including means (32) fordetermining a reference point on the drum so that said tachometergenerator will not begin to discharge said capacitor until saidreference point is reached.

3. A control system for a tire building machine including a cylindricaldrum and work devices wherein a first ply of fabric is wrapped aroundthe rotating drum and thereafter the work devices associated with thedrum sequentially perform operations upon the first ply and other tirecomponents comprising, input program means providing coded commandsrelating to a specific step in the tire building sequence, matrixdecoder means receiving and recognizing said coded commands andproviding outputs to activate circuitry to accomplish an operation inthe tire building sequence, timer means controlling an output of saidmatrix decoder means so that said output is provided only at selecttimes, drum control means capable of receiving an output of said matrixdecoder means and operating the tire building drum accordingly, andstitcher control means capable of receiving an output of said matrixdecoder means and operating a stitcher accordingly,

said stitcher control means including a position potentiometer means(62) providing a signal to a position servo means positioning thestitcher with respect to the drum,

said position servo means including error amplifier means receiving thesignal from said position potentiometer means (62) and feedbackpotentiometer means monitoring the position of the stitcher andproviding a feedback signal to said error amplifier means, and motorcontrol means (40) receiving the output of said error amplifier andpositioning the stitcher accordingly, the output of said error amplifierequaling zero when the stitcher is properly located according to thesignal from said position potentiometer means.

4. A control system for a tire building machine including a cylindricaldrum and work devices wherein a first ply of fabric is wrapped aroundthe rotating drum and thereafter the work devices associated with thedrum sequentially perform operations upon the first ply and other tirecomponents comprising, input program means providing coded commandsrelating to a specific step in the tire building sequence, matrixdecoder means receiving and recognizing said coded commands andproviding outputs to activate circuitry to accom plish an operation inthe tire buildin sequence, timer means controlling an output of salmatrix decoder means so that said output is provided only at selecttimes, drum control means capable of receiving an out put of said matrixdecoder means and operating the tire building drum accordingly, andstitcher control means capable of receiving an output of said matrixdecoder means and operating a stitcher accordingly,

said stitcher control means including operational amplifier means,tachometer generator means providing a signal which is the analog ofdrum speed to said amplifier means, and motor control means moving thestitcher according to the output of said amplifier means.

5. A control system according to claim 4 wherein lap ratio potentiometermeans adjusts the movement of the stitcher with respect to the speed ofthe drum.

6. A control system for a tire building machine including a cylindricaldrum and work devices wherein a first ply of fabric is wrapped aroundthe rotating drum and thereafter the work devices associated with thedrum sequentially perform operations upon the first ply and other tirecomponents comprising, input program means providing coded commandsrelating to a specific step in the tire building sequence, matrixdecoder means receiving and recognizing said coded commands andproviding outputs to activate circuitry to accomplish an operation inthe tire building sequence, timer means controlling an output of saidmatrix decoder means so that said output is provided only at selecttimes, drum control means capable of receiving an output of said matrixdecoder means and operating the tire building drum accordingly, andstitcher control means capable of receiving an output of said matrixdecoder means and operating a stitcher accordingly,

said stitcher control means including pressure error amplifier meansreceiving an input signal from pressure position potentiometer means,the setting of said pressure position potentiometer means representingthe position of the stitcher at which it is desired to change thepressure applied to the drum by the stitcher, feedback means monitoringthe position of the stitcher and providing a feedback signal to saidpressure error amplifier, and pressure switch means receiving the signalfrom said pressure error amplifier and changing the pressure of thestitcher when the desired position of the stitcher is reached.

1. A control system (10) for a tire building machine including acylindrical drum (11) and work devices wherein a first ply of fabric iswrapped around the rotating drum and thereafter the work devicesassociated with the drum sequentially perform operations upon the firstply and other tire components comprising, input program means (15)providing coded commands relating to a specific step in the tirebuilding sequence, matrix decoder means (16) receiving and recognizingsaid coded commands and providing outputs to activate circuitry toaccomplish an operation in the tire building sequence, timer means (20)controlling an output of said matrix decoder means so that said outputis provided only at select times, drum control means (30) capable ofreceiving an output of said matrix decoder means and operating the tirebuilding drum accordingly, said drum control means including integratingamplifier means (34) having a charging capacitor, position potentiometermeans (31) charging said capacitor with a charge representing thedesired amount of rotation of the drum, tachometer generator means (35)providing a signal which is the analog of drum rotation, said signalfrom said tachometer generator means discharging said capacitor, andmotor control means (40) rotating the drum as long as a charge appearsin said capacitor, whereby said drum is rotated according to the settingof said position potentiometer means, and work device control meanscapable of receiving an output of said matrix decoder means andoperating a work device accordingly.
 2. A control system according toclaim 1 including means (32) for determining a reference point on thedrum so that said tachometer generator will not begin to discharge saidcapacitor until said reference point is reached.
 3. A control system fora tire building machine including a cylindrical drum and work deviceswherein a first ply of fabric is wrapped around the rotating drum andthereafter the work devices associated with the drum sequentiallyperform operations upon the first ply and other tire componentscomprising, input program means providing coded commands relating to aspecific step in the tire building sequence, matrix decoder meansreceiving and recognizing said coded commands and providing outputs toactivate circuitry to accomplish an operation in the tire buildingsequence, timer means controlling an output of said matrix decoder meansso that said output is provided only at select times, drum control meanscapable of receiving an output of said matrix decoder means andoperating the tire building drum accordingly, and stitcher control meanscapable of receiving an output of said matrix decoder means andoperating a stitcher accordingly, said stitcher control means includinga position potentiometer means (62) providing a signal to a positionservo means positioning the stitcher with respect to the drum, saidposition servo means including error amplifier means receiving thesignal from said position potentiometer means (62) and feedbackpotentiometer means monitoring the position of the stitcher andproviding a feedback signal to said error amplifier means, and motorcontrol means (40) receiving the output of said error amplifier andpositioning the stitcher accordingly, the output of said error amplifierequaling zero when the stitcher is properly located according to thesignal from said position potentiometer means.
 4. A control system for atire building machine including a cylindrical drum and work deviceswherein a first ply of fabric is wrapped around the rotating drum andthereafter the work devices associated with the drum sequentiallyperform operations upon the first ply and other tire componentscomprising, input program means providing coded commands relating to aspecific step in the tire building sequence, matrix decoder meansreceiving and recognizing said coded commands and providing outputs toactivate circuitry to accomplish an operation in the tire buildingsequence, timer means controlling an output of said matrix decoder meansso that said output is provided only at select times, drum control meanscapable of receiving an output of said matrix decoder means andoperating the tire building drum accordingly, and stitcher control meanscapable of receiving an output of said matrix decoder means andoperating a stitcher accordingly, said stitcher control means includingoperational amplifier means, tachometer generator means providing asignal which is the analog of drum speed to said amplifier means, andmotor control means moving the stitcher according to the output of saidamplifier means.
 5. A control system according to claim 4 wherein lapratio potentiometer means adjusts the movement of the stitcher withrespect to the speed of the drum.
 6. A control system for a tirebuilding machine including a cylindrical drum and work devices wherein afirst ply of fabric is wrapped around the rotating drum and thereafterthe work devices associated with the drum sequentially performoperations upon the first ply and other tire components comprising,input program means providing coded commands relating to a specific stepin the tire building sequence, matrix decoder means receiving andrecognizing said coded commands and providing outputs to activatecircuitry to accomplish an operation in the tire building sequence,timer means controlling an output of said matrix decoder means so thatsaid output is provided only at select times, drum control means capableof receiving an output of said matrix decoder means and operating thetire building drum accordingly, and stitcher control means capable ofreceiving an output of said matrix decoder means and operating astitcher accordingly, said stitcher control means including pressureerror amplifier means receiving an input signal from pressure positionpotentiometer means, the setting of said pressure position potentiometermeans representing the position of the stitcher at which it is desiredto change the pressure applied to the drum by the stitcher, feedbackmeans monitoring the position of the stitcher and providing a feedbacksignal to said pressure error amplifier, and pressure switch meansreceiving the signal from said pressure error amplifier and changing thepressure of the stitcher when the desired position of the stitcher isreached.